Atherosclerosis is reproducibly induced in normocholesterolemic specific pathogen free (SPF) chickens by infection with Marek's disease herpesvirus (MDV). Uninfected chickens do not develop this arterial disease even when fed high levels of dietary cholesterol. The distribution and character of the artherosclerotic lesions have a striking resemblance to chronic human artherosclerosis. Since humans are known to be persistently infected with up to five herpesviruses the significance of these findings is apparent. Studies in progress, or planned, concern the possible viral mechanisms involved which lead to atherosclerosis. These will include comparative in vitro and in vivo studies on the nature of MDV injury to arterial cells. Studies are also planned to determine whether inoculation of birds with avirulent herpesvirus strains will have any effect on the development of arterial lesions in birds infected with virulent MDV, i.e. - will avirulent virus strains prevent the atherosclerotic lesions induced by virulent MDV strains?